The present invention relates generally to methods and apparatus for altering material. More particularly, the present invention describes methods and apparatus for thermally altering the near surface characteristics of a material with a high energy, repetitively pulsed ion beam.
A variety of techniques have been developed for thermally altering the near surface characteristics of a material using ion beam, electron beam, x-ray and laser technologies. Unfortunately, the dramatic expectations of such technologies have largely gone unfulfilled. In particular, the use of lasers for thermally altering the near surface characteristics of materials has met with only limited commercial success. The more significant reasons for such poor reception are: 1) high cost per area treated, 2) short (&lt;50 nm) deposition depths in metals, 3) high reflectivity of metal surfaces, 4) large variations in photon absorption leading to non uniform treatment due to defects and non-uniformities in treated surfaces, and 5) low power levels require the use of small (typically .ltoreq.1 cm.sup.2) beam spots which must then be swept across a surface to treat large areas which can lead to undesirable mechanical and electrical edge effects in surfaces treated with swept beams.
The use of ion beams for thermally altering the near surface characteristics of a material, while the most promising, has been fraught with the most substantial problems. Most notable of the limitations with existing ion beam technologies have been: 1) high costs per area treated, 2) the inability to generate a large number of pulses without the costly replacement of ion beam generator components, 4) low repetition rates, 5) low average power, and 6) the inability to reliably produce a uniform ion beam of a single selectable ion species. Typical ion beam generators use dielectric surface arcing on an anode as a source of ions and thereafter magnetically or geometrically direct and focus the generated ion beam onto the material of interest. This surface arcing (also called "flashover") destroys the anode surface in &lt;100 pulses, and produces a mixed species of ions that cannot be adjusted. Other difficulties arising from flashover include: the production of large quantities of neutral gas that makes high repetition rate difficult, generated debris can contaminate surfaces being treated, and non uniformity and irreproducibility of the beam in some cases due to the localized and difficult to control nature of flashover.
Present ion beam generators are typically "one shot" devices, i.e. they operate at repetition rates &lt;&lt;1 Hz. The principal limitations in operating existing ion beam generators at repetition rates &gt;&gt;1 Hz are threefold. First, the inability to repetitively generate high voltage (&gt;0.25 MeV), low impedance (&lt;&lt;100 .OMEGA.) high average power (&gt;10.sup.9 watts), electrical pulses in the .about.range of 30-500 nanoseconds in duration. Second, the inability of the ion beam generator to operate repetitively for an extended number of operating cycles (&gt;&gt;10.sup.3)without replacement of major components. Third, the inability to operate with electrical efficiencies &gt;5%. These limitations alone have made it impossible to consider industrial applications of the ion beam technology for surface treating materials.
The present apparatus for generating high energy, repetitive ion beams has over come the limitations of existing ion beam generators and provides a cost effective processing technology for thermally altering the near surface characteristics of materials.